This invention relates generally to an improved DC power supply which is coupled to a load having sensitive circuit elements, such as a radio or the like, and specifically to an improved transient overvoltage protection circuit utilized with a conventional DC power supply which acts to protect both the power supply elements and the load from overvoltages which may occur from transient electrical signals existing in the area adjacent the power supply. Oftentimes, when driving a load with a conventional DC power supply, transient electrical signals generated by an exterior source can be impressed in the power supply circuitry causing momentary but extremely large overvoltages on the power supply system and any load attached thereto, resulting in damage to either the power supply elements or the load or both. Sensitive semi-conductor elements downstream of the conventional DC power supply are often damaged from such transient signals, which require replacement in the load. Mutual coupling from adjacent circuits or the switching of adjacent electrical equipment (on or off) are examples of how transient signals can be induced into the DC power supply line. An example of a problem area in the past is found in the use of radio equipment in an aircraft or other vehicles having several electrical devices housed in compact areas. A secondary problem with a DC power supply has been that if the load, such as a radio, develops a short circuit, the DC power supply can be damaged.
The instant invention provides a protection circuit for a conventional DC power supply which protects both the DC power supply and the load against either transient overvoltages which may be induced into the DC power supply line or a short-circuit experienced in the load itself. The instant invention is characterized by having extremely positive and fast switching which provides a rapid and positive disconnect of the load from the power supply input when a transient overvoltage is impressed. The protection circuit includes a temperature compensated power supply disconnect switching network which stabilizes the current limit threshold.